1. Field of the Invention
The present invention relates to an optical microscope and a spectrum measuring method and, particularly, to an optical microscope and a spectrum measuring method with use of a spectroscope for measuring a spectrum.
2. Description of Related Art
Raman spectroscopy is advantageous in that measurement can be executed on a sample in any of gaseous, liquid, crystalline and amorphous solid forms, irrespective of whether temperature is high or low, without using a special measurement atmosphere such as a vacuum atmosphere. In addition, the Raman spectroscopy is advantageous in that no particular pretreatment of a sample is needed, and the sample can be measured as it is. Therefore, measurement has been done in many ways utilizing such advantages. The application of the Raman spectroscopy enables observation of molecules without staining and observation of impurities in a semiconductor.
To carry out the Raman spectroscopy, a Raman microscope using a spectroscope is disclosed (Japanese Unexamined Patent Publication Nos. 2002-14043 and 2003-344776). The Raman microscope focuses laser light onto a sample. The Raman spectroscopy then disperses Raman scattered light from the sample with use of the spectroscope to thereby measure a Raman spectrum. Further, the Raman microscope executes measurement while moving the sample to thereby measure the spatial distribution of Raman scattered light intensity at a particular wavelength.
Another Raman microscope is disclosed that linearly illuminates a sample by use of a cylindrical lens for shortening measurement time and detects Raman scattered light with a CCD camera (CHARLENE A. DRUMM and another, “Microscopic Raman Line-Imaging With Principal Component Analysis” APPLIED SPECTROSCOPY, 1995, Volume 49, Issue 9, pp. 1331-1337). Because the Raman microscope illuminates a sample in a line form, it is possible to illuminate a large area at a time and thus shorten measurement time. However, in the case where light is changed into a linear form by the cylindrical lens, it is difficult to uniformly apply light, causing a peripheral area to be darkened.
Furthermore, an optical microscope is disclosed that deflects laser light and conducts scanning (Japanese Unexamined Patent Publication No. 2007-179002 (Kobayashi et. al.)). The optical microscope includes an X-directional scanning unit and a Y-directional scanning unit. A scanning period of the Y-directional scanning unit is set shorter than exposure time of a camera mounted on a spectroscope (cf. paragraph 0042). It is thereby possible to measure a Raman spectrum of a linear area in one frame of the camera.
As described above, the microscopes disclosed in Kobayashi et al. and CHARLENE A. DRUMM et al. use the spectroscope for measuring a Raman spectrum. However, in such Raman microscopes, reflected light is imaged through the spectroscope by use of a spectroscope camera, which raises the following issue. In the spectroscope camera, for which low noise is demanded, reading speed is slow. It is thus difficult to perform imaging at a high speed with the spectroscope camera. Accordingly, the imaging time is longer compared to a camera that images normal reflected light.
Further, if the surface of a sample is not flat, focus is sometimes made on a space where the sample does not exist. Specifically, in the case of using a sample with an uneven surface, a focal position can be at a position different from the sample surface in some cases. Therefore, when measuring a Raman spectrum from the sample surface at a desired point of the sample, it is necessary to perform spectrum measurement a plurality of times by moving the sample in the Z direction at each point. This causes the issue that measurement of a Raman spectrum takes long time.
As described above, the optical microscope according to related art has the issue that the measurement time is long when using a spectroscope for measuring a Raman spectrum.
The present invention has been accomplished to address the above issues, and an object of the invention is thus to provide an optical microscope and a spectrum measuring method that enable measurement of a spectrum in a short time even in the structure of using a spectroscope for measuring a spectrum.